Best speaker brands for transient response

The cheap 'pro audio' systems that I have heard are painfully awful. Here too, it seems like you get what you pay for. Sometimes. YMMV

I've been running D9s for 6+ years and really love them.   Previous to the D9 was 3 years of Magico S1s, a quick trip with Cornwall IIIs, and then a few years of Revel F52s.   I like all of these speakers and they all sounded very fast and 'live' sounding to my ears.    The Magicos were crazy fast and resolving, snares sounded so life like to me, but they could also be fatiguing and although they had very musical bass, I missed the slam that my previous speakers had. 

When moving on from the S1s I tried the Harbeth 40.2 (among a few other British brands) and then the Spendor D9 and found the D9 to be a great fit between the two. Yes, the tweeter wasn't as resolving or as fast as the S1's tweeter, and their midrange wasn't as textured and rich as the 40.2, but they offered a good taste of what both speakers do best.  Don't sleep on a used pair of D9s; I've seen them go recently in the $4K range and I think that is a great value personally if you like the D series sound signature.   I have no idea how D9s compare to the newer 7.2s; but I like the idea of the dedicated midrange in the D9.

Regarding how they compare to newer models, I've recently demoed the Borresen X2 and I agree their tweeter sounded more detailed and ultimately refined than the D9s older design, but I personally preferred the Spendor's midrange to the X2 and although the X2 offers a lot of bass output for the size of the speaker, I didn't prefer it over the big Spendor's bass output which to me sounds more like a sealed box than a ported design; I actually think the X2's bass output would maybe be problematic in my room, at least with the distance I could place them from my rear wall.   The X2s sound signature reminded me a lot of the Vivid Kaya 45 which I also demoed at the same dealer a while back, super detailed and clean, with some midrange texture, but also with the ability to maybe be a little lean sounding depending on the equipment used.   These are obviously just my personal tastes and opinions. Many Harbeth fans like to tell me the D series is ungodly bright (or too 'modern' sounding).  Listening for yourself is definitely the way to go if possible...; cheers.

@ddafoe thank you for your response, that is super helpful.

I didn't prefer it over the big Spendor's bass output which to me sounds more like a sealed box than a ported design;

This is exactly what I'm looking for. I have two ported JBL models (not expensive, the Studio 590s and 4305Ps) and while they have many strengths, I much prefer to the bass signature of my sealed KLHs, although the active 4305Ps are pretty fast too.

I actually think the X2's bass output would maybe be problematic in my room, at least with the distance I could place them from my rear wall. 

This is my only concern with the X2s, the room probably is barely big enough for them in a best case scenario, based on recommended dimensions, and there's a good chance they won't be enjoyable off-axis at all. The recommended listening dimensions for the D7.2s is how I have my KLHs placed there now.

@deep_333 -- thank you for your response.

For example, Meyer Sound and pro Yamaha (specific models)

Do you find that the Yamaha pro strengths find their way into their premium home audio models like the NS 2000/5000?

Yamaha like many big brands with lots of money make both state of the art stuff and total junk. While I have not heard NS 5000, it leans toward state of the art and have a lot thought put into the materials. The tuning (they published measurements) seem bright on axis to me. They would need less toe in than typical speakers for me to enjoy them. Where the JBLs you are looking at have more of a rolled off treble and probably need listened to closer to on axis to sound neutral.

sadly I think the lower end JBLs are pretty average (still good) and are held back by the small compression drivers. You can seen the diaphragm breakup in the measurements and hear it as fatigue. I think the Revel counter parts are better. But at the highend I like JBL a lot better than Revel’s current offerings (I have owned a number of speakers from both brands and speak with experience). Once you get into “real” compression drivers it is a totally different game.